Case study: NSW vaccine effectiveness study

Ongoing assessment of COVID-19 vaccine effectiveness (VE) provides real-world evidence about the level of protection vaccination schedules offer against disease. Findings have informed vaccination policy in the context of an evolving pandemic and changing SARS-CoV-2 variants and supported public health messaging to maintain community confidence in the vaccination program.

This collaboration between the National Centre for Immunisation Research and Surveillance and NSW Health (Public Health Response Branch and the Centre for Epidemiology and Evidence) aimed to assess VE in the NSW population using linked routinely collected SARS-CoV-2 surveillance data. Five assessments were undertaken using different methods (Liu et al. 2022).

• Study 1 found that during the SARS-CoV-2 Delta wave, rates of infection were over 10-fold higher and intensive care unit admissions or deaths were more than 16-fold higher in the unvaccinated population compared with 2-dose vaccine recipients (≥12 years).
• Study 2 estimated VE of 72.8% (95% CI 76.1–82.1) against infection for 2-dose vaccine recipients (≥16 years) early in the Delta wave.
• Study 3, conducted over the entire Delta outbreak period (June-November 2021), estimated VE against hospitalisation in people aged ≥18 years (89.8%; 95% CI 88.8–90.7 at 14 or more days after dose 2).
• Study 4 reassessed VE following the emergence of Omicron due to its immune escape properties. Attack rates of >50% were reported in two indoor entertainment venue outbreaks where >95% of attendees had received 2 doses (an average of 2 months prior).
• Study 5 reported rapid waning of 2-dose VE against Omicron infection and, to a lesser extent, waning against hospitalisation/death in people aged ≥40 years. However, with a third dose effectiveness against infection was restored and protection against severe disease enhanced: compared to recent (<90 days) 2-dose vaccine recipients the relative VE for dose 3 was 7% (95% CI 5–9%) against infection and 65% (95% CI 61–69%) against hospitalisation/death.

This work provided the first estimates of VE in an Australian population using real-world data for NSW. Findings have informed state and Commonwealth policies about the need for, and timing of, the third dose booster and the importance of maintaining other public health measures. Outputs were presented to national disease control and vaccination policy committees and three reports were released publicly, with associated media and health communications. The work highlights the value of a routinely updated linked data resource to enable timely, ongoing vaccine program evaluations as population immunity and COVID-19 epidemiology changes.

References:

Liu B, Gidding H, Stepien S et al 2022, Relative effectiveness of COVID-19 vaccination with 3 compared to 2 doses against SARS-CoV-2 B.1.1.529 (Omicron) among an Australian population with low prior rates of SARS-CoV-2 infection, Lancet (preprint), DOI: 10.2139/ssrn.4142075.